(a) Field of the Invention
The present invention relates to a shift control method for a pneumatic shift system, and more particularly, to a shift control method for a pneumatic shift system in which a piston of a shift control device of the shift system is rapidly returned to a position effecting neutral shifting following driver manipulation of a gearshift lever to a neutral range from a drive range.
(b) Description of the Related Art
In trucks, buses and other such vehicles in which the engine is provided at the rear of the vehicle, because of the substantial distance between the transmission and the driver, a shift device is typically provided to convey clutch and gearshift lever operations to the transmission. A pneumatic shift system, rather than the conventional hydraulic or mechanical shift system, is being increasingly used to perform such a function. In the pneumatic shift system, air pressure is electronically controlled to change shift speeds and modes of the transmission.
FIG. 1 shows a schematic view of a typical pneumatic shift system to which the present invention is applied. FIG. 2 shows a schematic view of a shift control device and related elements shown in FIG. 1.
In the pneumatic shift system, a lever position sensor 6 detects driver manipulation of a gearshift lever 4L. The lever position sensor 6 outputs electrical signals corresponding to the change in position of the gearshift lever 4L to an electronic control unit (ECU 8), after which the ECU 8 outputs signals to control a magnetic valve assembly 10 to open and closed states according to the signals received from the lever position sensor 6. Accordingly, air is supplied to or exhausted from a shift control device 12 to control a transmission 14 into various forward and reverse shift speeds and modes.
The magnetic valve assembly 10 is connected to an air tank 15 and receives the supply of air from the air tank 15. Also, by the supply and exhaust of air from and to the air tank 15 via a reaction valve 18, which is a 3-way magnetic valve connected to a reaction cylinder (not shown), shift feeling is provided to the driver when the gearshift lever 4L is manipulated to different shift modes.
The ECU 8 is connected to a shift mode display 20, and the ECU 8 performs control such that the shift mode display 20 displays the present shift mode after receiving signals from the lever position sensor 6. The ECU 8 is also connected to a warning lamp 24 which alerts the driver of either shift failure caused by the incorrect supply of air to the magnetic valve assembly 10, or of the mis-operation of the gearshift lever 4L by the driver. The ECU 8 detects such problems through its connection with a shift mode sensor 22.
The shift control device 12 includes a first cylinder 26 and a second cylinder 28. Air is supplied to and exhausted from the first cylinder 26 and the second cylinder 28 by the operation of the magnetic valve assembly 10 which operates according to signals output from the ECU 8. The magnetic valve assembly 10 and the shift control device 12 are connected via air pipes 9 to enable such operation. A piston 30 is slidably disposed within the shift control device 12. The piston 30 is displaced in a rightward or leftward direction (in the drawing) according to the supply of air to the first cylinder 26 and the second cylinder 28.
A striker 32 is fixedly disposed on the piston 30. Accordingly, when the piston 30 is displaced in the leftward direction, the striker 32 is also moved such that it operates the transmission 14 to either a first, third or fifth speed of a drive range; and when the piston 30 is displaced in the rightward direction, the striker is moved such that it operates the transmission 14 to either a second or fourth speed of the drive range, or into reverse. That is, when the driver operates the gearshift lever 4L to different shift modes, the ECU 8 controls the magnetic valve assembly 10 so that air is supplied to or exhausted from the first cylinder 26 and the second cylinder 28 of the shift control device 12, thereby controlling the displacement of the piston 30 and the striker 32.
Accordingly, when the gearshift lever 4L is shifted into one of the drive ranges from the neutral range, starting from a state of equilibrium, compressed air is exhausted from either the first or second cylinder 26 and 28 such that smooth shifting is realized. However, when the gearshift lever 4L is shifted into the neutral range from one of the drive ranges, shifting is delayed by the operation of again obtaining a state of equilibrium by overcoming the force of compressed air acting in one direction.
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide a shift control method for a pneumatic shift system in which to effect shifting into neutral, compressed air is supplied to both cylinders of the pneumatic shift system following the rapid exhaust of compressed air from one of the two cylinders, thereby realizing rapid shifting into the neutral range.
To achieve the above object, the present invention provides a shift control method for a pneumatic shift system including the steps of determining if a gearshift lever is positioned in a neutral range after receiving gearshift lever position signals; controlling a first magnetic chamber of a magnetic valve assembly from ON to OFF for a predetermined time interval if the gearshift lever is in the neutral range; and controlling both the first magnetic chamber and a second magnetic chamber of the magnetic valve assembly to ON if the predetermined time interval has elapsed.